HEAT-BONDABLE WOVEN OR KNITTED FABRIC

Abstract: The invention provides an easily heat-bondable woven or knitted fabric for which neither sewing nor an adhesive agent is need. A woven or knitted fabric (A) is textured from warps (1), each consisting of 24 polyester (m.p.: 250°C) filaments of 50 deniers, and wefts (2), each consisting of polypropylene (m.p.: 160°C) filaments, say, 24 filaments of 50 deniers plus 24 filaments of 75 deniers, between which there is a melting point difference of at least 20°C. The sites of the fabric to be bonded together are heated under pressure at a temperature higher than or equal to 160°C and lower than or equal to 250°C. The polypropylene wefts melt to serve as an adhesive agent while the polyester warps remain intact.

Description: FIELD OF THE INVENTION This invention relates to a woven fabric used for making various textile products such as bags, which enables strong bond strength to be achieved with heat bonding yet with no need of sewing at least two woven fabric pieces. BACKGROUND TECHNIQUE As generally known so far in the art, woven fabrics are bonded together by machine-sewing. The bonding of woven fabrics made of synthetic fibers having thermoplasticity, too, is often carried out by conventional machine-sewing, except when thin woven fabrics not required to have strong bond strength are bonded together by a combined sealing and cutting technique. As well known in the art, machine-sewing is labor-intensive operations unsuitable for mass fabrication, and the combined sealing and cutting technique is practically unacceptable for lack of any bond strength, especially for lack of any sealing strength for woven fabrics of at least 40g/m2 in basis weight. JP-A-57-56780 discloses a woven fabric for belts wherein synthetic resin thread-like materials lower in melting point than synthetic fibers used for warp and weft by at least 30°C are textured along with warp and weft. It is directed to a woven fabric for use with belts and contemplates fusion bonding and fixing the warp and weft together in a single same fabric by heat treating the fabric. That is, JP-A-57-56780 addresses the art of fixing the texture of the fabric itself as a material for a belt. GB-A-2 247 696 discloses a woven fabric for use as a graft substrate formed by weaving warp and weft of fusible yarn and stiffer monofilament and heat set to bond the bicomponent fibers to orthogonal warp yarns to maintain integrity of the graft. Like JP-A-57-56780, GB-A-2 247 696 also contemplates heat setting the warp and weft together in a single fabric. Both of them contemplate to prevent deformation of a woven fabric at the intersection of the warp and weft to maintain the stable texture of the fabric. JP-A-4-033 977 discloses a woven fabric wherein yarns comprising a combined core and sheath type of composite fibers, and consisting of a core component polymer and a sheath component polymer lower in melting point than the core component by at least 20°C are used for at least one of warp and weft. This is directed to a substrate fabric for use as an adhesive tape and contemplates to enhance the workability and from stability of fabric by heat treating the fabric to soften the sheath component polymer into the form of a film to fusion bond the fibers together. EP-A-0 439 960 discloses a woven fabric consisting of a combined core and sheath type of composite filaments fabricated such that there is a melting point difference of at least 30°C between the core component and the sheath component. It is directed to a mesh woven fabric for use as a printing screen which is characterized in that after weaving is effected, the sheath component is fused to fusion bond the core yarns together of the warp and weft at the intersections of the warp and weft, whereby the texture of the fabric is integrated. WO-A-89-12707 discloses a netlike fabric comprising a three-layered flat yarn of a composite flat yarn in which the polymer melting point of the two outer layers is lower by at least 10°C than the polymer melting point of the intermediate layer, or a two-layer composite monofilament yarn having a sheath-core structure in which the polymer melting point of the sheath is lower by at least 10°C than the polymer melting point of the core. This patent again aims to enhance the bonding strength and prevent deformation of a woven fabric at the crossing points of the warp and weft. DE-A-2 739-782 discloses a woven or mesh fabric for use as a filter cloth having filtering openings, which is woven or knitted of a coated yarn of synthetic fibers coated with thermoplastic material in both the warp and weft directions, the coated yarn comprising a core yarn having high shearing strength and heat resistance and a coating yarn of thermoplastic polymer wrapped uniformly around and intimately bonded to the core yarn, wherein in the subsequent step the fabric is subjected to heat treatment at a temperature slightly higher than the melting point of the thermoplastic coating to provide precise and stable mesh openings to thereby allow for controlled superior filtering performance. This patent also aims to enhance the bonding strength and prevent deformation of a woven fabric at the crossing points of the warp and weft. As discussed above, the foregoing prior art references are all related to the stability of the texture of a single woven fabric itself, but none of them address the technique of heat bonding two pieces of woven fabric together by surface-to-surface bonding. Thus, what becomes a problem when woven fabrics are bonded together by heat-bonding yet without recourse to sewing is the bond strength of sites where they are bonded together. Films are bonded together over certain surfaces, while woven fabrics are bonded together at points. Under the same conditions, therefore, the woven fabrics are weaker than the films due to a bonded area difference between them. In the case of heat-bonding, woven fabrics must thus be wider in sealing area than films, etc. In other words, it is required to use a wider seal bar for heat-bonding purposes. Synthetic fibers of thermoplasticity are heat-bonded together with a temperature rise while they shrink by the action of heat. Therefore, when the temperature of a seal bar is kept higher than the heat-bonding temperature, no stable bonding of woven fabrics is achievable because they shrink concurrently upon coming into contact with the seal bar. An object of the present invention is to provide a woven fabric which enables textile products having the necessary and sufficient bond strength to be fabricated by a heat-bonding technique while they are kept from shrinkage. DISCLOSURE OF THE INVENTION In one aspect, the present invention provides a woven fabric which is textured from raw yarns consisting of at least two types of synthetic fiber yarns of thermoplasticity, said fabric being woven of warps and wefts, wherein yarns of either one of the warps and wefts have a melting point lower than that of the other of the warps and wefts with a melting point difference of at least 20°C therebetween; characterized in that at least two pieces of said woven fabric are heat bonded together with no need for sewing or adhesives when the pieces of said woven fabric are heated under pressure at a temperature higher than the melting point of either one of said two types of yarns having a lower melting point and lower than the melting point of the other type of yarns having a higher melting point. In another aspect, the present invention provides a woven fabric which is textured from at least two types of synthetic fiber yarns of thermoplasticity, said fabric being woven of warps and wefts, wherein yarns of either one of the warps and wefts have a combined core and sheath structure, said sheath being lower by at least 20°C in melting point than said core; characterized in that at least two pieces of said woven fabric are heat bonded together with no need for sewing or adhesives when the pieces of said woven fabric are heated under pressure at a temperature higher than the melting point of either one of said two types of yarns having a lower melting point and lower than the melting point of the other type of yarns having a higher melting point. In the texture of the woven fabric, two or more types of yarns having a certain melting point difference or yarns consisting of cores and sheaths are incorporated. When the sites of the woven fabric to be bonded together is heated under pressure at a temperature higher than the low melting point of one type of yarns and lower than the high melting point of the other type of yarns, the lower melting point yarns melt to have bonding action while the higher melting point yarns serve to keep the lower melting point yarns from shrinkage that would otherwise occur within the period during which the lower melting point yarns soften and finally melt, so that the texture of the bonded sites can be maintained constant in terms of dimensional stability. The melting point difference of at least 20°C is here understood to define a temperature difference for keeping the high-melting yarns from softening and shrinkage when the woven fabric is heated under pressure at the low-melting temperature. BRIEF DESCRIPTION OF THE DRAWING Figure 1 shows the texture of one preferable woven fabric according to this invention. BEST MODE FOR CARRYING OUT THE INVENTION The present invention will now be explained more specifically with reference to the accompanying drawing. Figure 1 is a partly plan view of the texture of one embodiment of the woven fabric according to the present invention. The woven fabric shown in Figure 1 is textured from two types of yarns having a certain melting point difference. As an illustrative example, the woven fabric is textured from warps 1, each consisting of 24 polyester (m.p.: 250°C) filaments A of 50 deniers, and wefts 2, each consisting of 24 polyester (m.p.: 250°C) filaments A of 50 deniers plus 24 polypropylene (m.p.: 160°C) filaments B of 75 deniers. When the sites of the fabric to be bonded together are heated under pressure at a temperature higher than or equal to 160°C and lower than or equal to 250°C, the polypropylene yarns B serve as an adhesive agent while the polyester yarns A remain intact. It is here to be understood that while the wefts are formed of yarns having a certain melting point difference in the above mentioned example, such yarns may be used for either warps or wefts. In this case, the melting point of the sheaths is lower than those of warps 1 and the cores of the wefts 2. Upon heated under pressure, the sheaths of the wefts 2 serve as an adhesive agent while the cores of the wefts 2 remain intact. It is to be noted that Figure 1 is directed to an example where one yarn is separated into a core and sheath for the purpose of illustration alone, but such yarn may be separated into any desired parts or the like. APPLICABILITY OF THE INVENTION TO INDUSTRY As explained above, the woven fabric according to the present invention is textured from yarns varying in melting point or yarns having a combined core and sheath structure, so that it can be heat-bonded with its texture and dimensional stability remaining intact, while the yarns having a lower melting point are used as an adhesive agent. Over conventional fabrics fabricated by heat-bonding using an adhesive film or otherwise sewing, therefore, the instant fabric is much more improved in terms of fabrication cost and time and, hence, operation efficiency. Therefore, the instant fabric is best suited for products to be bonded at numerous sites, for instance, bags.

Claims: A woven fabric which is textured from at least two types of synthetic fiber yarns of thermoplasticity, said fabric being woven of warps and wefts, wherein yarns of either one of the warps and wefts have a melting point lower than that of the other of the warps and wefts with a melting point difference of at least 20°C therebetween; characterized in that at least two pieces of said woven fabric are heat bonded together with no need for sewing or adhesives by heating the pieces of said woven fabric under pressure at a temperature higher than the melting point of the one of said two types of yarns having a lower melting point and lower than the melting point of the other type of yarns having a higher melting point. A woven fabric which is textured from at least two types of synthetic fiber yarns of thermoplasticity, said fabric being woven of warps and wefts, wherein yarns of either one of the warps and wefts have a combined core and sheath structure, said sheath being lower by at least 20°C in melting point than said core; characterized in that at least two pieces of said woven fabric are heat bonded together with no need for sewing or adhesives by heating the pieces of said woven fabric under pressure at a temperature higher than the melting point of the one of said two types of yarns having a lower melting point and lower than the melting point of the other type of yarns having a higher melting point.

Inventors: NOTO SHINSUKE, TAMURA MAKOTO, TANAKA TOYOAKI, NOTO, SHINSUKE, TAMURA, MAKOTO, TANAKA, TOYOAKI, NOTO, Shinsuke, Kohei Co., Ltd., TANAKA, Toyoaki, Marubeni Co., Ltd.
Applicants: KOHEI CO LTD, KOHEI CO., LTD.
Application year: 1994
Main classification: D03D15
IPC codes: D03D15